When one intends to print a confidential document, it is undesirable for a random person in the office who happens to be walking by to see the document or a coworker to pick up and carry away the document by mistake. One way to avoid this undesirable situation is to require that identification information is entered into a printing device or an MFP. This identification information needs to be authenticated using a password or other means of identification. However, existing solutions regarding identification, authentication, and secure communication do not address the problem of a malicious attack by sending a large amount of print jobs to a mailbox to which the malicious sender has no authorization. Also unsolved is the problem of an interceptor of a print job analyzing the intercepted print job to obtain the decryption key and using the decryption key to read the other jobs from the same originating user. The present invention arose out of the above perceived needs and concerns associated with secure communication of printing jobs involving destination mailboxes.